1. Technical Field
The present disclosure relates to the electronic field. More in particular, the disclosure concerns a current-controlled resistor.
2. Description of the Related Art
An attenuator is an electronic device commonly used in wireless applications at high frequencies, for example at radio-frequencies (RF) or microwaves (more in general a frequency in the range between 10 Mhz and 2 Ghz); the attenuation of the attenuator is variable in order to control automatically the voltage level of a high-frequency input signal.
It is known that forward biased Positive-Intrinsic-Negative (PIN) diodes are used in the design of radio-frequencies or microwaves attenuators having a variable attenuation, wherein at least one PIN diode is used for controlling automatically the voltage level of an input RF signal. In fact, at high frequencies a PIN diode is equivalent to a current-controlled resistor, that is, it operates as a variable resistor having a resistance value controlled by the forward bias current flowing in the PIN diode, the resistance value being inversely proportional to the forward bias current; for example, the minimum resistance value of the PIN diode is 10 Ohm and the maximum resistance value is 1500 Ohm.
FIG. 1 shows a current-controlled resistor 1 according to the prior art. The current-controlled resistor 1 comprises:
an input terminal I101 for receiving a RF input signal;
a control input terminal I103 for receiving from a current source IE102 a variable bias control current I for controlling the small signal resistance value between the input terminal I101 and ground and between the input terminal I101 and the control input terminal I103;
a series connection of two forward biased PIN diodes D100, D101 connected between the current source IE102 and ground GND (PIN diodes D100, D101 are enclosed in FIG. 1 by a square for distinguishing with respect to a PN diode).
The series connection of the two forward biased PIN diodes D100, D101 implement two variable resistors, each one having a variable resistance value controlled by the bias control current I.
The current-controlled resistors according to the prior art have the disadvantage to require the use of at least one PIN diode, which is a device which can't be simply implemented into an integrated circuit, because additional process steps are necessary for the formation of the intrinsic layer of the PIN diode in standard technologies (such as Bipolar, CMOS or BiCMOS technologies).